Actually I semi lied, Spotting telescope PF-65ED II, can be mated with a converter and fitted to Pentax DSLRs and becomes 780mm F6 lens

It is actually a 780mm f/12.5 lens. You could also couple the same PF-CA35 adapter ($400) to a Pentax PF-100ED spotting scope ($1600) to get a whopping 12.5/1250mm telephoto lens, a focal length equivalent to 1844mm in 35mm terms, guaranteed to be almost unusable, except to shoot the moon